He will also retain the title of Hitachi GST chief financial officer.
Milligan is a 23-year veteran of the technology industry. He was most recently senior vice president and CFO for Western Digital where he played a key role in helping the company deliver profitability, diversify its revenue base and achieve industry-leading cash and asset efficiencies.
Prior to that he worked at Dell and Price Waterhouse.
According to Hiroaki Nakanishi, chairman and chief executive officer of Hitachi GST, Milligan will be instrumental in redefining the company's business model, increasing operational efficiency and overseeing its business transformation.
Nakanishi will remain as chairman of Hitachi GST to strengthen GST and Hitachi Ltd. He will also be made executive vice president responsible for Hitachi Group's global strategy.
"As president, (Milligan) is responsible for maximizing our investments, while delivering long-term value to our customers and sustained growth for Hitachi GST," he said.
"Moving forward, I am also very excited about my new assignment within Hitachi, Ltd. I'll be leveraging my experience from transforming Hitachi GST into a successful business as I work to position Hitachi Group as a thriving global company with extensive reach and range."
Hitachi GST is making two other executive management changes to further strengthen the relationship with Hitachi, Ltd:
Shinjiro Iwata, executive vice president Hitachi GST has been named CEO of Service and Global Business for the Information and Telecommunication Systems Group of Hitachi, Ltd.
Masaya Watanabe will be joining Hitachi GST as chief strategist of Data Storage. He was previously general manager of the Enterprise Server Division within the Information & Telecommunication Systems Group at Hitachi, Ltd.
Milligan will be based at the company's San Jose, California headquarters.